Ultrasonic sensor

ABSTRACT

An ultrasonic sensor, that transmits probe waves which are ultrasonic waves and acquires detection waves including reflected waves which have been reflected from surrounding objects, includes a transmitter/receiver that transmits the probe waves and acquires the detection waves, a detection wave processing section that executes processing for passing a predetermined frequency band which includes the frequency of the probe waves, an amplitude measurement section which measures the amplitude of the detection waves, and a judgement section which judges whether there is adherence of foreign matter on the transmitter/receiver, based on a relationship between a time axis and values of the amplitude of the detection waves during a reverberation interval following the termination of transmitting the probe waves.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application is based upon and claims priority of theprior Japanese Patent Application No. 2016-113866, filed in Japan PatentOffice on Jun. 7, 2016, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to an ultrasonic sensor that transmitsultrasonic waves as probe waves, and acquires reflected waves that arereflected from objects in the surroundings, with the reflected wavesincluding detection waves.

BACKGROUND ART

In the prior art, ultrasonic sensors have been implemented whichtransmit ultrasonic waves as probe waves, receive reflected waves thatare reflected from an object, and detect the distance of the object.With such an ultrasonic sensor, when foreign matter such as water or thelike adheres to a transmitter/receiver which performs transmission ofthe probe waves and reception of the detection waves, there is a dangerthat errors will arise in the calculated distances of objects, or anobject may be judged to exist where it does not, or it may be judgedthat there is no object when an object actually does exist. Hence, it isnecessary to be able to judge whether or not there is foreign matteradhering to the transmitter/receiver.

An ultrasonic sensor which judges when there is foreign matter adheringto the transmitter/receiver is disclosed in PTL 1. With the ultrasonicsensor disclosed in PTL 1, judgement as to whether or not there isforeign material adhering to the transmitter/receiver is made by using atime point at which an amplitude falls below a set threshold value.

CITATION LIST Patent Literature

[PTL 1] Japan Patent Publication No. 2015-40837

SUMMARY OF THE INVENTION

In a case where foreign matter such as water or mud adheres to thesurface of the ultrasonic sensor, a change will occur in frequency dueto the effects of the mass, etc., of the foreign matter. In general withan ultrasonic sensor, the amplitude is acquired after passing a receivedsignal through a bandpass filter for removal of noise, and hence, ifthere is a change in the reverberation frequency, the amplitude will notdecrease gradually but will vary in a stepwise manner. Thus, with theultrasonic sensor of PTL1, it is not possible to accurately obtain timepoint at which the amplitude falls below the threshold value, and hence,it is difficult to accurately judge whether or not there is adherence offoreign matter.

The present disclosure is intended to overcome the above problem, havinga main objective of providing an ultrasonic sensor which can accuratelyjudge when there is foreign matter adhering to the surface of atransmitter/receiver.

The present disclosure relates to an ultrasonic sensor that transmitsprobe waves which are ultrasonic waves and acquires detection wavesincluding reflected waves that are reflected from surrounding objects,and includes a transmitter/receiver that transmits the probe waves andacquires the detection waves, a detection wave processing section thatexecutes processing for passing a predetermined band of frequencieswhich include the frequency of the probe waves, an amplitude measurementsection which measures the amplitude of the detection waves, and ajudgement section that judges the adherence of foreign matter on thetransmitter/receiver, based on a relationship between a time axis andvalues of the amplitude of the detection waves during a reverberationinterval which follows the termination of transmitting the probe waves.

In a case where there is no foreign matter adhering to thetransmitter/receiver, then the frequency of a reverberation, which isproduced following termination of transmitting the probe waves, will beclose to the frequency of the probe waves. In that case, even whenprocessing for passing a prescribed band of frequencies is executed bythe detection wave processing section on the detection waves, inacquiring the amplitude of the reverberation, the detection waves willnot be readily attenuated. On the other hand, if there is foreign matteradhering to the transmitter/receiver, then the frequency of thereverberation that is produced following termination of transmitting theprobe waves will differ from the frequency of the probe waves. In thatcase, when processing for passing a prescribed band of frequencies isexecuted by the detection wave processing section, in acquiring theamplitude in the reverberation interval, detection waves that areoutside the prescribed band of frequencies will become attenuated andthe accompanying amplitude will become small. Hence, if foreign matteris adhering to the transmitter/receiver, then the amplitude will becomesmaller than when there is no foreign matter adhering, and thiscondition of the amplitude being small will continue during thereverberation interval. With the above configuration, a decision as towhether foreign matter is adhering to the transmitter/receiver is madebased on a relationship between time and amplitude in the reverberationinterval following termination of transmitting the probe waves, andhence, even if processing is executed on the detection waves for passinga prescribed band of frequencies, the adherence of foreign matter can beaccurately detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objectives, features and advantages of the presentdisclosure will be made clearer from the following detailed description,referring to the appended drawings.

FIG. 1 is a configuration diagram of an ultrasonic sensor;

FIG. 2 shows waveforms for a case in which foreign matter does notadhere to a transmitter/receiver, with (a) being the waveform offrequency and (b) being the waveform of amplitude;

FIG. 3 shows waveforms for a case in which foreign matter adheres to thetransmitter/receiver, with (a) being the waveform of frequency and (b)being the waveform of amplitude;

FIG. 4 is a flow chart of processing executed by the ultrasonic sensor;

FIG. 5 is a diagram for describing processing relating to a secondembodiment, for the case in which foreign matter does not adhere to thetransmitter/receiver;

FIG. 6 is a diagram for describing processing relating to the secondembodiment, for the case in which foreign matter adheres to thetransmitter/receiver;

FIG. 7 is a diagram for describing processing relating to a thirdembodiment, for the case in which foreign matter does not adhere to thetransmitter/receiver;

FIG. 8 is a diagram for describing processing relating to the thirdembodiment, for the case in which foreign matter adheres to thetransmitter/receiver;

FIG. 9 is a diagram for describing processing relating to a fourthembodiment, for the case in which foreign matter does not adhere to thetransmitter/receiver;

FIG. 10 is a diagram for describing processing relating to the fourthembodiment, for the case in which foreign matter adheres to thetransmitter/receiver;

FIG. 11 is a diagram for describing processing relating to a fifthembodiment, for the case in which foreign matter does not adhere to thetransmitter/receiver; and

FIG. 12 is a diagram for describing processing relating to the fifthembodiment, for the case in which foreign matter adheres to thetransmitter/receiver.

DESCRIPTION OF THE EMBODIMENTS Description of Embodiments

The present embodiment of an ultrasonic sensor is installed on a mobilebody such as a vehicle or the like. An object detection system, whichincludes the ultrasonic sensor that transmits probe waves in each ofprescribed control periods, receives reflected waves that are reflectedfrom an object in the surroundings of the mobile body, and measures thetime duration between transmission and reception, for thereby obtainingthe distance between the mobile body and the object.

FIG. 1 is a configuration diagram of an ultrasonic sensor 10 of thepresent embodiment. The ultrasonic sensor 10 is connected forcommunication with an ECU 20 which controls respective functions of thevehicle, with the ultrasonic sensor 10 being controlled based oncommands from the ECU 20, and transmitting detection results to the ECU20.

A control section 11 communicates with the ECU 20, and executes controlfor transmitting probe waves which are ultrasonic waves, based oncommands from the ECU 20, while also transmitting to the ECU 20 thedetection results of detection waves that include reflected waves. Atthat time, the ECU 20 notifies the control section 11 of the frequencyof the probe waves, and the control section 11 drives atransmitter/receiver 12 such as to transmit ultrasonic waves having thatfrequency.

The transmitter/receiver 12 is of known type, being equipped with apiezoelectric element and a drive circuit which supplies drive power tothe piezoelectric element, with the drive power being supplied by thetransmitter/receiver 12 to the piezoelectric element by means of controlsignals from the control section 11, for transmitting probe waves thatare ultrasonic waves.

The transmitter/receiver 12 in addition receives, as detection waves,reflected waves that are reflected from objects in the surroundings, andalso receives other ultrasonic waves as detection waves. The detectionwaves received by the transmitter/receiver 12 are inputted to thedetection wave processing section 13 as voltages.

A detection wave processing section 13 performs filter processing of thedetection waves. Specifically, filter processing of the detection wavesis executed using a bandpass filter having a passband that can pass aband of frequencies which include the frequency of the probe waves,attenuating the amplitude of detection waves that are at frequenciesother than those of the band of frequencies passed by the bandpassfilter. The reason for this is that, when probe waves are reflected froman object and the reflected waves are acquired as detection waves, thefrequency of the reflected waves will be close to the frequency of theprobe waves, while detection waves having a different frequency have ahigh possibility of being noise. The detection wave processing section13 inputs the voltage value to an amplitude measurement section 14,after filter processing.

The amplitude measurement section 14 measures the amplitude of theacquired detection waves. Specifically, to acquire the amplitude, avalue of voltage that is obtained based on the detection waves isconverted to the amplitude. In detecting the amplitude, an upper limitvalue is determined for the voltage that can be acquired, and if theacquired voltage has a value exceeding the upper limit, the amplitude ismade the upper limit value Amax.

The amplitude that is measured by the amplitude measurement section 14will be explained referring to FIGS. 2 and 3, based also on thefrequency of the detection waves. The frequencies shown in FIGS. 2(a)and 3(a) are obtained, for example, by taking the points at which thevoltage changes from positive to negative as zero crossing points, andcalculating the inverse of the period between the zero crossing pointsas a frequency. The frequency count values in the diagrams show themeasured numbers of reference waves between the zero crossing points ofthe detection waves. That is to say, if the value of the frequency countbecomes large, this signifies that the time between the zero crossingpoints becomes longer and that the frequency becomes lower.

Since the amplitude of the ultrasonic waves is obtained as analternation between positive and negative values, the positive peaks foreach frequency define the amplitude at that frequency. FIGS. 2(b) and3(b) show connected amplitudes that are maximum positive values for therespective frequencies, that is to say, these diagrams show the resultof envelope detection.

As described above, the detection wave processing section 13 performsprocessing for attenuating waves having frequencies other than those ofthe prescribed frequency band of the bandpass filter. Hence, if foreignmatter adheres to the surface of the transmitter/receiver 12 and causesthe frequency in the reverberation interval to change, then as shown inFIG. 3(a), the amplitude will be attenuated by the bandpass filter, andthe amplitude will be reduced by comparison with the case in which thereis no adherence of foreign matter, as shown in FIG. 3(b). If judgementis made based only on whether or not the amplitude is small, then it isnot possible to determine whether the amplitude has become small due toadhering foreign matter, or has become small due to the fact that thereverberation interval has ended. However, if the amplitude remainsabove a prescribed value during a prescribed range of time, then it isjudged that there is adhering foreign matter. It should be noted thatthe foreign matter may include snow, water, mud, etc., while theexpression “adhering” can signify a condition in which water is flowingon the surface of the transmitter/receiver 12.

As shown in FIGS. 2(b), 3(b), a first threshold value Ath1 and a secondthreshold value Ath2, which is smaller than the first threshold valueAth1, are set. The specific values of the first threshold value Ath1 andthe second threshold value Ath2 are determined through experiment, andare set by a threshold value setting section 15 and inputted to a timersection 16.

The timer section 16 measures, as a first interval ΔT1, an interval forwhich the amplitude is higher than the first threshold value Ath1, andmeasures, as a second interval ΔT2, an interval for which the amplitudeis higher than the second threshold value Ath2. The amplitude maymomentarily fall below the first threshold value Ath1, due to errors indetecting the amplitude, etc., even when there is no foreign matteradhering to the transmitter/receiver 12. Furthermore, the amplitude mayin some cases momentarily fall below the second threshold value Ath2,when there is foreign matter adhering to the transmitter/receiver 12,even during the reverberation interval. Hence, for the first intervalΔT1 and the second interval ΔT2, it would be equally possible toterminate the time measurement on condition that the amplitude has beenbelow the first threshold value Ath1 or the second threshold value Ath2continuously during a prescribed sampling period.

A judgement section 17 calculates the time that elapses from the pointat which the amplitude falls below the first threshold value Ath1 untilit falls below the second threshold value Ath2. Specifically, thejudgement section 17 acquires the first interval ΔT1 and the secondinterval ΔT2 from the timer section 16, and subtracts the first intervalΔT1 from the second interval ΔT2. A decision is then made as to whetheror not the calculated interval is a value that is greater than aprescribed value. If the calculated value is greater than the prescribedvalue, then it can be said that the amplitude in the reverberationinterval has remained above the prescribed value during a time intervalthat is within the prescribed range. Hence, the judgement result istransmitted to the control section 11.

When the control section 11 acquires a judgement result from thejudgement section 17 indicating that there is adherence of foreignmatter, processing is then executed for notifying this to a driver ofthe vehicle. Specifically, the judgement result is transmitted to theECU 20, and the driver of the vehicle is notified by use of a displayapparatus, etc., installed in the vehicle. It should be noted that theprocessing which is executed when it is judged that there is foreignmatter adhering to the transmitter/receiver 12 is not limited to thisexample, and it would be equally possible to execute various other formsof processing.

The processing sequence executed by the ultrasonic sensor 10 will bedescribed referring to the flow chart of FIG. 4. The processing of theflow chart of FIG. 4 is executed repetitively at each of prescribedsampling periods.

Firstly, in step S101, the detection waves are acquired, and then instep S102, the amplitude is measured. In step S103, a decision is madeas to whether or not the time measurement of the first interval ΔT1 isin progress. It is possible to judge in this way whether or not thevalue of the first interval ΔT1 is zero. Step S103 can be performed byjudging whether the value of the first interval ΔT1 is not zero, or byjudging a flag which indicates that the time measurement of the firstinterval ΔT1 is in progress. As described above, since the timemeasurement of the first interval ΔT1 and that of the second intervalΔT2 are started concurrently, if the time measurement of first intervalΔT1 is in progress, then the time measurement of the second interval ΔT2is also in progress.

If there is a positive judgement decision in step S103, that is to say,the time measurement of the first interval ΔT1 is not in progress, thenthe processing proceeds to step S104, in which a decision is made as towhether or not the time measurement of the second interval ΔT2 is inprogress. In the same way as for step S103, step S104 can be performedby judging whether the value of the second interval ΔT2 is not zero, orby judging a flag which indicates that the time measurement of thesecond interval ΔT2 is in progress.

If there is a negative decision in step S104, that is to say, the timemeasurement of the second interval ΔT2 is not in progress, processingthen proceeds to step S105, in which a decision is made as to whetherthe amplitude measured in step S102 is higher than the first thresholdvalue Ath1. As described above, processing proceeds to step S105 if anegative decision is reached in both step S103 and step S104, so thatreaching a positive decision in step S105 is limited to the case inwhich the amplitude exceeds the first threshold value Ath1 for the firsttime after transmitting of the probe waves has started. A negativedecision in step S105 is reached in an interval which extends from thestart of transmitting the probe waves until the amplitude reaches thefirst threshold value Ath1, or in an interval which follows the time atwhich the amplitude falls below the second threshold value Ath2, that isto say, an interval which follows the end of the of the reverberationinterval.

If there is a positive decision in step S105, that is to say, if it isjudged that the amplitude exceeds the first threshold value Ath1, thenthe time measurement of the first interval ΔT1 and the second intervalΔT2 is started, and the processing sequence is then ended. Step S106 inthe processing sequence is executed at time point t1 shown in FIGS. 2and 3. On the other hand, in a case in which there is a positivedecision made in step S105, that is to say, it is judged that theamplitude is not greater than the first threshold value Ath1, then theprocessing sequence is ended directly.

If there is a positive decision in step S103, that is to say, in a casein which the time measurement of the first interval ΔT1 is in progress,then processing proceeds to step S107, in which a decision is made as towhether or not the amplitude exceeds the first threshold value Ath1. Ifthere is a positive decision in step S107, that is to say, the amplitudethat has been measured in step S102 is greater than first thresholdvalue Ath1, then processing proceeds to step S108, in which the firstinterval ΔT1 and second interval ΔT2 are incremented. That is to say,the time measurement of the first interval ΔT1 and second interval ΔT2is continued. Step S108 of the processing sequence is executed in aninterval that extends from after time point t1 until time point t2,shown in FIGS. 2 and 3. The processing sequence is then ended.

If there is a negative decision in step S107, that is to say, if theamplitude that was measured in step S102 is less than the firstthreshold value Ath1, then processing proceeds to step S109. In stepS109 the value of the first interval ΔT1 is stored in temporary memory,and in the succeeding step S110, incrementing of the second interval ΔT2is performed. The time measurement of the second interval ΔT2 iscontinued, while ending the time measurement of the first interval ΔT1.Step S110 of the processing sequence is executed in the next samplingperiod after time point t2, shown in FIGS. 2 and 3. The processingsequence is then ended.

If there is a positive decision in step S104, that is to say, if thetime measurement of the first interval ΔT1 has ended and the timemeasurement of the second threshold value Ath2 is in progress, thenprocessing proceeds to step S111, in which a decision is made as towhether or not the amplitude is greater than the second threshold valueAth2. If there is a positive decision in step S111, that is to say, ifthe amplitude measured in step S102 is greater than the second thresholdvalue Ath2, then processing proceeds to step S112, in which incrementingof the second interval ΔT2 is performed. That is to say, the timemeasurement of the second interval ΔT2 is continued. Step S112 of theprocessing sequence is executed in an interval that extends from afterthe next sampling period following time point t2, shown in FIGS. 2 and3, up to time point t3. The processing sequence is then ended.

If there is a negative decision in step S111, that is to say, if theamplitude measured in step S102 is less than the second threshold valueAth2, then processing proceeds to step S113. In step S113, the value offirst interval ΔT1 that has been temporarily stored in memory issubtracted from the value of the second interval ΔT2 whose timemeasurement has been completed, and a decision is made as to whether theresultant value is greater than a prescribed value. That is to say, adecision is made as to whether or not the length of the interval forwhich the amplitude is less than the first threshold value Ath1 andabove the second threshold value Ath2 is greater than a prescribedvalue. Step S113 of the processing sequence is executed in the nextsampling period following time point t3, shown in FIGS. 2 and 3.

If there is a positive decision in step S113, that is to say, if thelength of the interval for which the amplitude is less than the firstthreshold value Ath1 and above the second threshold value Ath2 isgreater than the prescribed value, then processing proceeds to stepS114, and a judgement is made as to whether or not there is foreignmatter adhering to the surface of the transmitter/receiver 12. Theprocessing sequence is then ended. However, if there is a negativedecision in step S113, then the processing sequence is ended directly.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides the following effects.

If there is foreign matter adhering to the transmitter/receiver 12, thenthe frequency of a reverberation that is produced following thetransmitting of the probe waves becomes different from the frequency ofthe probe waves. If filter processing is performed by the detection waveprocessing section 13 at that time, then since detection waves that areat frequencies outside the passband of the filter will becomeattenuated, the amplitude will be reduced. For that reason it can beconsidered that if the amplitude is greater than the first thresholdvalue Ath1, then the frequency during the reverberation interval isclose to the frequency when transmitting the probe waves, while if theamplitude is smaller than the second threshold value Ath2 then it can beconsidered that the reverberation interval has ended. On the other hand,if an interval continues during which the amplitude is less than thefirst threshold value Ath1 and is greater than the second thresholdvalue Ath2, then it can be assumed that the interval is thereverberation interval and that the frequency in that interval deviatesfrom that of the probe waves. With the present embodiment, the timeinterval which elapses from the point at which the amplitude falls belowthe first threshold value Ath1 until it falls below the second thresholdvalue Ath2 is acquired, and by judging whether or not that interval islonger than a prescribed interval, a decision can be made as to whetheror not the frequency during the reverberation interval deviates from thefrequency of the probe waves. Hence, an accurate judgement can be madeas to whether or not there is foreign matter adhering to thetransmitter/receiver 12.

Second Embodiment

The present embodiment differs from the first embodiment with respect toa part of the processing executed by the judgement section 17.Specifically, the judgement section 17 acquires a number of times thatlocal maximums of the amplitude are attained in a prescribed intervalfollowing the time at which the amplitude falls below the firstthreshold value Ath1. This number of occurrences of local maximums istaken to be the number of times that the amplitude changes from anincreasing to a decreasing condition. It should be noted that if theamplitude, after having once increased then remains constant, andthereafter decreases, then this can be taken as being a singleoccurrence of a local maximum value.

The judgement section 17 compares the counted number of local maximumsof the amplitude with a predetermined value. If the number of localmaximums is greater than the predetermined value, then it is judged thatthere is adherence of foreign matter.

The processing applied to the amplitude with the present embodiment willbe described referring to FIGS. 5 and 6. In FIGS. 5 and 6, the positionswhere there are local maximums are surrounded by dashed lines.

As shown in FIG. 5, if there is no foreign matter adhering to thetransmitter/receiver 12, then the time at which the amplitude fallsbelow the first threshold value Ath1 is time point t11 at which thereverberation interval ends. After falling below the first thresholdvalue Ath1 at time point t11, the amplitude thereafter continues todecrease, and a condition is reached at which it is hardly possible todetect the amplitude. For that reason, in a prescribed intervalbeginning from time point t11 and elapsing at time point t12, theacquired number of local maximums of the amplitude becomes small.

On the other hand, as shown in FIG. 6, if there is foreign matteradhering to the transmitter/receiver 12, then time point t11 at whichthe amplitude falls below the first threshold value Ath1 is the time atwhich transmitting the probe waves is ended. Since the interval ofattenuation following time point at which the amplitude falls below thefirst threshold value Ath1 is a continuation of the reverberationinterval, the amplitude repetitively increases and decreases in thevicinity of a certain value. For that reason, the acquired number oflocal maximums attained by the amplitude becomes large during aprescribed interval which extends from time point t11 and elapses when acertain time point t12 is reached.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides the following effects, in addition to effectssimilar to those provided by the ultrasonic sensor 10 of the firstembodiment.

If there is no foreign matter adhering to the transmitter/receiver 12,then when the amplitude falls below the first threshold value Ath1, thissignifies that the reverberation interval has ended, so that theamplitude will continue to gradually decrease after having fallen belowthe first threshold value Ath1, until the value can hardly be detected.For that reason, the acquired number of local maximums of the amplitudewill become small. On the other hand, if there is foreign matteradhering to the transmitter/receiver 12, then when the amplitude fallsbelow the first threshold value Ath1, this signifies that thetransmission of probe waves has ended, and during the reverberationinterval thereafter the amplitude will repetitively increase anddecrease, and hence, the number of local maximums of the amplitude willincrease. Hence, by counting the number of local maximums during aprescribed interval extending from time point at which the amplitudefalls below the first threshold value Ath1, a judgement can be made asto whether or not there is foreign matter adhering to thetransmitter/receiver 12.

Third Embodiment

The present embodiment differs from the first embodiment with respect toa part of the processing executed by the judgement section 17.Specifically, the judgement section 17 provides a prescribed period inthe reverberation interval, and obtains the number of times that localmaximum value of amplitude are attained during that prescribed period.The prescribed period is set such as to include at least part of thereverberation interval, and with the present embodiment, the prescribedperiod commences when the transmitting of the probe waves is ended. Theprocessing for obtaining the number of times that local maximum value ofamplitude are attained are the same as for the second embodiment, sothat specific description is omitted.

The processing of the amplitude with the present embodiment will next bedescribed, referring to FIGS. 7 and 8. In FIGS. 7 and 8, time point t21is the start of an interval in which the number of local maximums iscounted and which ends at time point t22. In FIGS. 7 and 8, as for thesecond embodiment, the locations of the local maximums are enclosed bydashed lines.

If there is no foreign matter adhering to the transmitter/receiver 12,as shown in FIG. 7, the amplitude will generally be maintained close toan upper limit value Amax during the reverberation interval, and willbecome attenuated when the reverberation interval terminates. For thatreason, the number of local maximums that are obtained in the intervalfrom t21 to t22 will become small.

On the other hand, if there is foreign matter adhering to thetransmitter/receiver 12, as shown in FIG. 7, then the amplitude willrepetitively increase and decrease in the vicinity of a certain valueduring the reverberation interval. For that reason, the number of localmaximums obtained during the interval from t21 to t22 becomes large.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides the following effects, in addition to effectssimilar to those provided by the ultrasonic sensor 10 of the firstembodiment.

In the processing executed for obtaining the amplitude of the detectionwaves, an upper limit value Amax is provided for the value that can beobtained, and if the actual amplitude is greater than the upper limitvalue Amax, processing is executed for setting the amplitude of thedetection waves as the upper limit value Amax. If there is no foreignmatter adhering to the transmitter/receiver 12, then since theattenuation of the amplitude of the detection waves during thereverberation interval is small, the amplitude becomes the upper limitvalue Amax. Hence, the number of local maximums of the amplitude becomessmall. On the other hand, if there is foreign matter adhering to thetransmitter/receiver 12, then the attenuation of the amplitude of thedetection waves during the reverberation interval will be relativelygreat, so that the amplitude becomes smaller than Amax. Hence, if thereis foreign matter adhering to the transmitter/receiver 12, the number oflocal maximums of the amplitude will become greater than for the case inwhich no foreign matter adheres, so that a judgement can be made as towhether or not there is adherence of foreign matter, from the number ofthese local maximums.

Fourth Embodiment

The present embodiment differs from the first embodiment with respect toa part of the processing executed by the judgement section 17. Theprocessing executed by the judgement section 17 of the presentembodiment will be described referring to FIGS. 9 and 10.

The judgement section 17 obtains an area S that is enclosed by theenvelope which extends from the point at which the amplitude falls belowthe first threshold value Ath1 up to the point at which it falls belowthe second threshold value Ath2. Specifically, the amplitudes at each ofrespective sampling periods are accumulated, and the cumulative value isset as the area S.

The judgement section 17 judges whether or not the calculated area S isgreater than a prescribed value. If the area S is greater than theprescribed value, then it is judged that there is matter such as wateradhering to the transmitter/receiver 12, and that judgement result isnotified to the control section 11.

It should be noted that when the area S is obtained surrounded by anenvelope as with the present embodiment, it would be equally possible toset a prescribed interval following the point at which the amplitudefalls below the first threshold value Ath1, as with the secondembodiment, and to obtain the area S for that interval.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides the following effects, in addition to effectssimilar to those provided by the ultrasonic sensor 10 of the firstembodiment.

If there is foreign matter is adhering to the transmitter/receiver 12,then the frequency during the reverberation interval becomes changed,and the duration of the interval from the point at which the amplitudefalls below the first threshold value Ath1 up to the point at which itfalls below the second threshold value Ath2 becomes increased. As aresult, the area S enclosed by the envelope of amplitudes will becomelarger. With the present embodiment, since a decision is made as towhether or not the area S enclosed by that envelope is greater than aprescribed value, a judgement can be made as to whether or not thefrequency during the reverberation interval deviates from the frequencyof the probe waves. Hence, it becomes possible to accurately judgewhether or not there is foreign matter is adhering to thetransmitter/receiver 12.

Fifth Embodiment

The present embodiment differs from the above embodiments with respectto a part of the processing executed by the judgement section 17. Theprocessing executed by the judgement section 17 of the presentembodiment will be described referring to FIGS. 11 and 12.

The judgement section 17 provides a plurality of prescribed intervalswhich follow the point at which the amplitude falls below the firstthreshold value Ath1. With the present embodiment, there are 4prescribed intervals provided, having respectively identical lengths ofperiod. Areas S1 to S4 are calculated for the respective periods. Theprocessing for calculating these areas S1 to S4 is the same as that forthe area S of the fourth embodiment.

The judgement section 17 next calculates the amounts of change in theareas S1˜S4. In doing this, the average of the amounts of change betweenthe areas S1˜S4 may be used, or the difference could be obtained betweenthe area S1 having the largest value and the area S4 having the smallestvalue, or the differences between the areas that are mutually precedingand succeeding could be obtained, and the largest one of thesedifferences used. Furthermore, it would be equally possible to obtain anapproximate function based on the values of the areas S1˜S4 and toperform judgement based on the approximate function. For each of thesecases, if there is adherence of foreign matter, the amount of change inarea will be greater than when foreign matter is not adhering. Hence, adecision can be made as to whether there is adherence of foreign matter,by comparing the value of the amount of change in area with a prescribedvalue, and determining that there is adherence of foreign matter if thevalue of the amount of change in area is greater than the prescribedvalue.

It should be noted that in the processing for setting the plurality ofperiods with the present embodiment, the prescribed intervals can extendfrom time point at which the probe waves are terminated, as with thethird embodiment. In that case, if there is no adherence of foreignmatter, the amplitude will greatly decrease when the reverberationinterval ends, so that if the change in area is small, it can be judgedthat there is adherence of foreign matter.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides the following effects, in addition to effectssimilar to those provided by the ultrasonic sensor 10 of the firstembodiment.

If there is foreign matter is adhering to the transmitter/receiver 12,then the amplitude during the reverberation interval becomes attenuated.Hence, by obtaining a plurality of areas S1˜S4 that are enclosed byamplitude envelopes, and judging whether or not these areas are becomingattenuated, a decision can be made as to whether there is foreign matteradhering to the transmitter/receiver 12.

Sixth Embodiment

The present embodiment differs from the above embodiments with respectto a part of the processing executed by the judgement section 17. Withthe present embodiment, the judgement section 17 compares a part of thedetection waves with a reference waveform, which has been predetermined.The reference waveform is a waveform that has been measured beforehandin a case in which there is no foreign matter adhering to thetransmitter/receiver 12. If the correlation between the waveform of thedetection waves and the reference waveform is obtained and thecorrelation value is greater than a prescribed value, then since it canbe said that the shape of the waveform of the detection waves is closeto that of the reference waveform, it is judged that there is no foreignmatter adhering to the transmitter/receiver 12. On the other hand, ifthe correlation value is smaller than the prescribed value, then sinceit can be said that the shape of the waveform of the detection wavesdeviates from that of the reference waveform, it is judged that there isforeign matter adhering to the transmitter/receiver 12.

It should be noted that although a waveform which is measured beforehandin a condition in which there is no foreign matter adhering to thetransmitter/receiver 12 is used here as the reference waveform, it wouldbe equally possible to use, as the reference waveform, a waveform forthe case in which there is foreign matter adhering to thetransmitter/receiver 12. Furthermore, it would be equally possible toprovide beforehand a waveform for the case in which there is foreignmatter adhering to the transmitter/receiver 12 and a waveform for thecase in which there is no adherence of foreign matter, respectively, andto judge which of these waveforms is closest in shape to the waveform ofthe detection waves.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides effects that are similar to those provided by theultrasonic sensor 10 of the first embodiment.

Seventh Embodiment

The overall configuration of the present embodiment is similar to thatof the first embodiment, with a part of the processing being different.With the present embodiment, the detection wave processing section 13 isprovided with two bandpass filters having respectively different widthsof passband. The center frequency of each of these bandpass filters isthe frequency of the detection waves. It should be noted that in thefollowing description, the bandpass filter having the narrower one ofthe passbands is referred to as the first bandpass filter, and thebandpass filter having the wider passband is referred to as the secondbandpass filter.

The detection wave processing section 13 executes, in parallel,processing for passing the acquired detection waves through the firstbandpass filter and through the second bandpass filter. Next, theprocessing of the flow chart shown in FIG. 4 is applied to the detectionwaves that have passed through the first bandpass filter and have passedthrough the second bandpass filter, respectively, with the intervalduring which the amplitude is smaller than the first threshold valueAth1 and is greater than the second threshold value Ath2 beingrespectively obtained for these, that is to say, the value resultingfrom subtracting the first interval ΔT1 from the second interval ΔT2 isobtained. The respective calculated values are then compared, and adecision is made as to whether or not there is foreign matter adheringto the transmitter/receiver 12.

If there is no foreign matter adhering to the transmitter/receiver 12,then since the frequency of the detection waves during the reverberationinterval will be close to the frequency of the probe waves, theamplitudes of the respective detection waves which pass through thebandpass filters will not become readily attenuated, irrespective ofwhich of the filters is passed through. Hence, the value obtained bysubtracting the first interval ΔT1 from the second interval ΔT2 will besubstantially the same for the detection waves that are passed by thefirst bandpass filter and the detection waves that are passed by thesecond bandpass filter.

If there is foreign matter adhering to the transmitter/receiver 12, thensince the frequency of the detection waves during the reverberationinterval will be different from the frequency of the probe waves, thedetection waves that pass through the first bandpass filter will have arelatively high degree of attenuation in amplitude, while the degree ofamplitude attenuation of the detection waves that pass through thesecond bandpass filter will be relatively small. Hence, the valueobtained by subtracting the first interval ΔT1 from the second intervalΔT2 will be greater for the detection waves that are passed by thesecond bandpass filter.

It should be noted that it would be equally possible to apply processingfor effecting passing of detection waves through two bandpass filters,as performed with the present embodiment, to the second and thirdembodiments. That is to say, instead of comparing the number of localmaximums of the amplitude with a predetermined value, it would beequally possible to compare the respective numbers of local maximums ofthe amplitude of detection waves that have passed through bandpassfilters having different passbands, and judgement could be performed byusing the difference between them.

Furthermore, it would be equally possible to apply processing foreffecting passing of detection waves through two bandpass filters, asperformed with the present embodiment, to the fourth embodiment. Ifthere is no foreign matter adhering to the transmitter/receiver 12, thenthe frequency during the reverberation interval will be close to thefrequency of the probe waves, and hence, even when the detection waveshave been passed through bandpass filters having passbands that aredifferent from one another, the variation of amplitude with time will beclosely similar between the detection waves, and the correlation valuewill be relatively large. On the other hand, if there is foreign matteradhering to the transmitter/receiver 12, then the variation of amplitudewith time will be different between them, so that the correlation valuewill be relatively small. Hence, a judgement can be made as to whetheror not there is adherence of foreign matter.

Due to the above configuration, the ultrasonic sensor 10 of the presentembodiment provides effects that are similar to those provided by theultrasonic sensor 10 of the first embodiment, and also provides thefollowing effects.

When the detection waves are passed through a bandpass filter having awide passband, then irrespective of whether or not the frequencydeviates from the center frequency, the amplitude will not besignificantly attenuated. On the other hand, if the detection waves areprocessed by means of a bandpass filter having a narrow passband, thenif the frequency deviates from the center frequency, the amplitude willbe relatively greatly attenuated. Hence, it is possible to judge whetheror not there is foreign matter is adhering to the transmitter/receiver12 by comparing detection waves that have passed through bandpassfilters having respectively different passbands.

Modified Examples

With the above embodiments, in addition to using the relationshipbetween amplitude and time, it would be possible to also use frequencyin judging whether or not there is foreign matter adhering to thetransmitter/receiver 12. Specifically with each of the aboveembodiments, the judgement conditions are set as a first condition, anda second condition which is whether or not a frequency deviates from thefrequency of the probe waves, with the first condition and the secondcondition being used in judging whether or not foreign matter isadhering to the transmitter/receiver 12. It should be noted that itwould be equally possible for the second condition to include arequirement relating to time, for each of the above embodiments.

With the first embodiment, the time measurement of the first intervalΔT1 and the second interval ΔT2 is started on condition that theamplitude falls below the first threshold value Ath1. However, it wouldbe equally possible to commence the time measurement of the firstinterval ΔT1 and the second interval ΔT2 at time point of commencementof transmitting the probe waves.

With the first embodiment, time measurement of the first interval ΔT1and the second interval ΔT2 is performed, and the difference between themeasured values is obtained. However, it would be equally possible toset, as a required condition for starting the time measurement, that theamplitude is less than the first threshold value Ath1 and is greaterthan the second threshold value Ath2, and to set, as a requiredcondition for ending the time measurement, that the amplitude is lessthan the second threshold value Ath2. In that case, the judgement as towhether or not there is adhering foreign matter can be performed bycomparing the measured value of time with a prescribed value.

With the above embodiments, bandpass filters are used; however, it wouldbe equally possible to use band-stop filters instead. Furthermore, sincethe frequency becomes lower if there is foreign matter adhering to thetransmitter/receiver 12, it would be equally possible to use detectionwaves that have been passed through a high-pass filter, in theprocessing for judging whether or not there is adhering foreign matter.This is similarly true for the fifth embodiment, where it would beequally possible to use high-pass filters or band-stop filters havingrespectively different passbands.

With the second embodiment, the number of local maximums of theamplitude is obtained during a predetermined interval which commenceswhen the amplitude becomes less than the first threshold value Ath1.However, it would be equally possible to obtain the number of localmaximums during an interval in which the amplitude is less than thefirst threshold value Ath1 and is greater than the second thresholdvalue Ath2. As shown by the first embodiment, that interval, in whichthe amplitude is less than the first threshold value Ath1 and is greaterthan the second threshold value Ath2, is longer when there is foreignmatter adhering to the transmitter/receiver 12 than when there is noadhering foreign matter. Furthermore, since, if there is no adheringforeign matter, the amplitude will generally decrease monotonically fromthe point at which it becomes less than the first threshold value Ath1until it becomes less than the second threshold value Ath2, so that thepossibility of producing maximum values is low. Hence, judgement canaccurately be made as to whether or not foreign matter is adhering tothe transmitter/receiver 12, by obtaining the number of local maximumsof the amplitude during the interval in which the amplitude is less thanthe first threshold value Ath1 and is greater than the second thresholdvalue Ath2.

With the second embodiment, instead of obtaining the number of localmaximums, it would be equally possible to perform the judgement as toadhering foreign matter on the transmitter/receiver 12 by using thehighest-magnitude one of the local maximums, or by using the averagemagnitude of the local maximums, etc. If there is no foreign matteradhering to the transmitter/receiver 12, then since in that case thepoint at which the amplitude becomes less than the first threshold valueAth1 is the termination of the reverberation interval, the amplitudewill continue to become attenuated thereafter, until a condition isreached where it can hardly be detected. For that reason, the maximumamplitude will be small. On the other hand, if there is foreign matteradhering to the transmitter/receiver 12, then the point at which theamplitude becomes less than the first threshold value Ath1 is thetermination of transmitting the probe waves, and the amplitude willrepetitively increase and decrease during the reverberation intervalthereafter, so that there will be relatively large maximum values of theamplitude. Hence, a decision can be made as to whether foreign matter isadhering to the transmitter/receiver 12, from the maximum value of theamplitude during a predetermined interval that follows the point atwhich the amplitude becomes less than the first threshold value Ath1.

With the third embodiment, instead of using the number of localmaximums, it would be equally possible to judge whether foreign matteris adhering to the transmitter/receiver 12 by using the highest one ofthe local maximums of the amplitude, or by using the average of thelocal maximums, etc. Since the attenuation of the amplitude during thereverberation interval will be relatively small if no foreign matter isadhering to the transmitter/receiver 12, there will be a relativelylarge maximum value of the amplitude during that interval, while ifthere is foreign matter adhering to the transmitter/receiver 12 thenthere will be a relatively high degree of attenuation of the amplitudeduring the reverberation interval, so that the maximum value of theamplitude will be relatively small. Hence, a decision can be made as towhether foreign matter is adhering to the transmitter/receiver 12, fromthe maximum value of the amplitude during a predetermined interval thatfollows the termination of transmitting the probe waves.

With the fifth embodiment, processing is performed using bandpassfilters, in parallel, having respectively different passbands. However,it would be equally possible to perform processing for passing thedetection waves through bandpass filters which have respectivelydifferent transmission intervals, for example a preceding and asucceeding transmission interval.

With the fifth embodiment, two bandpass filters having respectivelydifferent passbands are used; however, it would be equally possible touse three or more bandpass filters. Moreover, it would be equallypossible to compare detection waves that have been passed by filtershaving respectively different functions. For example, the detectionwaves passed by a bandpass filter could be compared with the detectionwaves passed by a high-pass filter, or compared with the detection wavespassed by a band-stop filter.

The ultrasonic sensor 10 of the embodiments is installed on a mobilebody such as a vehicle; however, the ultrasonic sensor 10 is not limitedto such installation, and could be installed on a stationary object suchas a road structure or the like.

The present disclosure has been described based on embodiments, however,it should be understood that the disclosure is not limited to theembodiments or their configurations. The present disclosure incorporatesvarious modifications and equivalences within its scope. Furthermore,other combinations and forms, including single elements or more, arecontained in the scope and concepts of the present disclosure.

1. An ultrasonic sensor that transmits probe waves which are ultrasonicwaves, and acquires detection waves that include reflected waves whichhave been reflected from surrounding objects, comprising: atransmitter/receiver that transmits the probe waves and acquires thedetection waves; a detection wave processing section that executesprocessing for passing a predetermined frequency band which includes thefrequency of the probe waves; an amplitude measurement section thatmeasures the amplitude of the detection waves; and a judgement sectionthat judges whether there is adherence of foreign matter on thetransmitter/receiver, based on a relationship between a time axis andvalues of the amplitude of the detection waves during a reverberationinterval following the termination of transmitting the probe waves. 2.The ultrasonic sensor according to claim 1, wherein the judgementsection acquires, as the relationship between the time axis and theamplitude, an interval extending from the point at which the amplitudefalls below a first threshold value until the amplitude falls below asecond threshold value, and executes the judgement based on the acquiredinterval.
 3. The ultrasonic sensor according to claim 1, wherein thejudgement section provides, as the time axis, a prescribed interval thatfollows the point at which the amplitude falls below a threshold value,and the judgement section acquires a count of a number of local maximumsof the amplitude in the prescribed interval, and executes the judgementbased on that count.
 4. The ultrasonic sensor according to claim 1,wherein the judgement section provides, as the time axis, a prescribedinterval that follows the point at which the amplitude falls below athreshold value, and the judgement section executes the judgement basedon the maximum value of the amplitude in the prescribed interval.
 5. Theultrasonic sensor according to claim 1, wherein the judgement sectionprovides, as the time axis, a prescribed interval that followstermination of transmitting the probe waves, and the judgement sectionacquires a count of a number of local maximums of the amplitude in theprescribed interval, and executes the judgement based on that count. 6.The ultrasonic sensor according to claim 1, wherein the judgementsection provides, as the time axis, a prescribed interval that followsthe termination of transmitting the probe waves, and the judgementsection executes the judgement based on the maximum value of theamplitude in the prescribed interval.
 7. The ultrasonic sensor accordingto claim 1, wherein the judgement section acquires, as the relationshipbetween the time axis and the amplitude, an area enclosed by an envelopeof values of the amplitude, and executes the judgement based on thatarea.
 8. The ultrasonic sensor according to claim 7, wherein thejudgement section acquires the area after the amplitude has fallen belowa threshold value, and executes the judgement based on that area.
 9. Theultrasonic sensor according to claim 7, wherein the judgement sectionacquires respective areas for each of prescribed intervals, followingtermination of transmitting the probe waves, and executes the judgementbased on changes in the areas.
 10. The ultrasonic sensor according toclaim 1, wherein the judgement section sets an upper limit value to thevalues that can be acquired for the amplitude, and when the amplitude ofthe detection waves is greater than the upper limit value, makes theamplitude of the detection waves the upper limit value.
 11. Theultrasonic sensor according to claim 1, wherein the judgement sectionexecutes the judgement by comparing a relationship between the time axisand the amplitude that is based on the acquired detection waves with apredetermined relationship between the time axis and the amplitude. 12.The ultrasonic sensor according to claim 1, wherein the detection waveprocessing section is equipped with a plurality of filters which passrespectively different frequency bands, and the judgement sectioncompares the relationships between the time axis and the amplitude forthe respective outputs passed by the different filters, and executes thejudgement by means of the comparison result.
 13. The ultrasonic sensoraccording to claim 1, wherein the judgement section acquires thecorrelation value between a waveform expressing the time-axis variationof the amplitude and a waveform serving as a reference, and executes thejudgement by means of the correlation value.
 14. The ultrasonic sensoraccording to claim 1, wherein the detection wave processing section isequipped with a plurality of filters which pass respectively differentfrequency bands, and the judgement section acquires a correlation valuebetween respective waveforms that express the time-axis variation of theamplitudes passed by the different filters, and executes the judgementby means of the correlation value.
 15. The ultrasonic sensor accordingto claim 1, wherein the ultrasonic sensor further acquires the frequencyof the probe waves, the judgement section compares the acquiredfrequency with a frequency that serves as a reference frequency of theprobe waves, and the ultrasonic sensor executes the judgement by using afirst condition that is based on time and amplitude, and a secondcondition that is based on frequency.